from functools import reduce

class MathTools(object):
    @staticmethod
    def char2num(s):
        return {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}[s]

    @staticmethod
    def str2int(s):
        return reduce(lambda x, y: x * 10 + y, map(MathTools.char2num, s))